Hydraulic tappet



April 2l, 1959 P. F. BERcs/IANNv 8 2,882,876

Y HYDRAULICTAPPET Filed March 2a, 1957 2 sheets-sheet y1 INVENTOR.

y PAUL F. BERGMANN B% ATTORN EYS April Zlv, 1959 P. F BERGMANN' 1 2,882,876

HYDRAULIC TAPPET Filed March 28, 1957 INVENToR. PAUL F. BERGMANN ATTORNEYS United States Patent() HYDRAULIC TAPPET Paul F. Bergmann, Muskegon, Mich., assiguor to Johnson Products, Inc., Muskegon, Mich., a corporation of Michigan Application March 28, 1957, Serial No. 649,213

11 Claims. (Cl. 12S-#90) This invention relates to tappets and more particularly to hydraulic tappets.

The problem of properly actuating the valves of an explosion engine has always presented a problem. The valves are actuated by cams and it is necessary that the valve actuating mechanism or valveA train maintain constant contact with its actuating ca-m. However, during the initial period of operation of -a cold engine, the temperature rise of the various parts involved in the valve train causes appreciable change in its length. For the purpose of eliminating noise and wear, it is desirable that each component of the train maintain contact at all times. Thus, it is desirable to provide a self-compensating unit within the mechanism which automatically adjusts to decrease the length of the actuating mechanism as its temperature rises and increase the length when the engine has cooled. For many years hydraulic tappets have been used for this purpose.

Conventional hydraulictappets operate on the principle of transmitting the energy of the cam through hydraulic uid trapped in a chamber behind a plunger. During each operation of the cam, as the mechanisms length increases due to temperature, small amounts of the hydraulic lluid are permitted to escape the pressure chamber, thus eifecting adjustment in the position of the plunger and of the total length of the valve train.

In the conventional tappet, this leakage or leakdown is etlected and controlled solely through the lit between the plunger and the walls of the tappet body or housing. For effective operation, the leakdown must be precisely controlled and thus the t betweenr the plunger and the tappet body must be held to very close tolerances, normally limited to O.0002-0.00V023 of an inch. Such close tolerances require selective iitting of the plunger to the tappet body. Conventional practice is to sort these in increments of 33 millionths or 50 millionths of an inch.

ICC

ventional tappets, the leakdown occurs as the tappet is raised and lowered by the cam in actuating the valve. In this arrangement, the t of the plunger to the body was a compromise to provide the proper leakdown for the most extreme situation. It was unable to `adjust in response to variations in operating conditions deviating from this one norm. The tappet of this invention adjusts its length only after the valve has been closed and thus while the tappet is stationary. Consequently, it makes all adjust- .ments simultaneously and in response to the particular conditions then existing. It adjusts its length precisely during each cycle, eliminating any secondary adjustment. This avoids the diculties of secondary readjustment characteristic of conventional tappets. y

These and other objects and purposes of this invention will be immediately understood by those acquainted with the design and construction ofhydraulic/ tappets upon reading the following specification and the accompanying drawings.

In the drawings:

Fig. l is a central, sectional view of the tappet just before the cam starts to raise it.

Fig. 2 is a partially broken view of the tappet just after initiation of its rise under the inuence of the cam.

Fig. 3 is a :partially4 broken side elevation view of the tappet just after it has returned to its stationary position and during the tappets adjustment in eiiective length.

Fig. 4 is an oblique exploded view ofthe tappet.

Fig. 5 is a fragmentary, central, sectional view of a modiied construction for the tappet. I

Fig. 6 is a fragmentary, central, sectional view of a further modilied construction of a tappet. n

Fig. 7 is a bottom view of the rod seats illustrated in Figs. 5 and 6. p

In executing the objects and purposes of this invention, there has been provided a tappet having a hollow tappet body lopen at one end. It is of substantially conventional design. Within the tappetbody is a plunger, which at the vblind end of the tappet body, forms a pressure chamber and on the other side of the plunger a reservoir for hydraulic uid. One end of the plunger is equipped with a valve for Iadmitting hydraulic fluid from the reservoir into the pressure chamber when lthe supply in the latter falls below operating requirements. The outer end of the reservoir is closed by a rod seat. Between the rod seat and the adjacent end of the plunger is a valve arrangement biased llhis in itself is an expensive operation and even though increases the price of the tappets as well as the complexity of their manufacture.

This invention, for the iirst time, overcomes this diiiiculty because it does not depend upon leakdown to control its operation. This invention, for the first time, utilizes a valve structure to control the escape of hydraulic iluid from the pressure chamber. Thus, the permissible tolerances of lit between the plunger andthe Vtappet body may be greatly increased. In fact, fits of 0.005-0.006 of an inch are acceptable. The necessity for selective tit is eliminated along with the necessity for precision manufacture. It also permits the elimination of certain precision machining operations heretofore considered unavoidable.

This invention provides a tappet operating entirely differently from any tappet heretofore developed. In coninto closing position against the end of the plunger by a spring. Free communication is provided through the valve between the reservoir and an oil supply. At the periphery of the valve is a secondary pressure chamber communicating with the main pressure chamber. One wall of the secondary pressure chamber is formed by the valve. When the rod seat is released by the valve spring and the pressure in the pressure chamber is above a predetermined value, this pressure provides an opening force against the relief valve to permit the ow of hydraulic fluid from the secondary pressure chamber into the reservoir. The spring between the rod seat and the relief valve normally biases the relief valve closed. j

Referring specifically to the drawings, the numeral 1 indicates a tappet having a tappet body 2 slidably seated in a housing 2 such as a motor block (Fig. l). The housing 3 has an oil supply channel 4 communicating with an elongated, external circumferential channel 5 in the tappet body 2. The length of the channel 5 assures continued communication between the channel and the passage 4 as the tappet body reciprocates within the plunger 10. The interior of the plunger 10 is hollow,

Aforming a reservoir 11 communicating at its lower end with a passage 12. The passage 12 opens through the lower end of the plunger into the primary pressure chamber 13 between the end of the plunger and blind end of the tappet body. The passage 12, where it enters into the pressure chamber 13, is closed by a disk valve 14 biased into closing position by a spring 15. The valve is so arranged that it will open when the pressure in the reservoir 11 exceeds that in the pressure chamber 13.

The lower end of the spring 15 seats against the lower end of a cap 16 (Figs. l and 4). The cap 16 has an aperture 17 in its terminal end and side apertures 18. It is rigidly ailixed to the plunger by press fitting over the wall 19 on the lower end of the plunger. The plunger is biased away from the closed end of the tappet body by a plunger return spring 20.

The other or upper end of the plunger is of reduced external diameter forming an annular pressure cavity or secondary pressure chamber 25. The secondary pressure chamber 25 communicates with the primary pressure chamber 13 through leakage between the interior surfaces of the tappet body 2 and the exterior surfaces of the plunger 10. While this clearance is not suiricient to allow unrestricted flow of the hydraulic uid between the two chambers, it is suicient that the ow is rapid and adequate to allow practically instantaneous balancing of the pressures in the two chambers. In this connection it must be borne in mind that even large adiustments in tappet length are so small that only very small quantities of liquid are involved in each movement. In a tappet constructed according to this invention, the clearance between the plunger and the inside surface of the tappet body may be as much as .005 or .006 of an inch. This will allow adequate freedom of flow of the hydraulic uid between the two pressure chambers for the small quantities of hydraulic lluid` involved in the operation of the tappet. This compares with a clearance of 0.0002 to 0.00023 of an inch in the case of conventional tappet constructions.

The upper end of the plunger 10 is machined to form a smooth and accurate valve seat 26 for cooperation with the relief valve consisting of the sealing ring 27 and the valve plate 28. The sealing ring 27 is of a resilient material such as neoprene suitable for use in the presence of hydraulic fluids and related liquid hydrocarbons. Its outer periphery bears tightly against the wall of the tappet body 2 and forms a liquid seal with these walls past which only insignicant quantities of hydraulic uid will leak even under high operating pressures.

rThe sealing ring 27 cooperates with the valve seat 26 on the end of the plunger and forms a liquid tight seal therewith. The sealing ring is supported and backed by the valve plate 28 which is disk shaped and extends almost to the inner walls of the tappet body, thereby supporting the sealing ring against distortion between it and the body wall when the secondary pressure chamber 25 is under high elevated pressures. The valve plate 28 is apertured at 29, providing free communication from the oil passage 4 ot the reservoir 11.

Seated within the tappet housing 2 and above the valve plate 28 is the rod seat 35, The rod seat has a somewhat spherically formed external opening 36 for reception of the end of the rod 37. 'Ihe upper periphery of the rod seat extends outwardly to the inner walls of the tappet body and makes a sliding, liquid restraining seal with these walls. The outer diameter of the lower or inner portion is of reduced diameter to provide an annular passage 38 communicating both with the apertures 29 in the valve plate 28 and with the opening 39 in the tappet body. This provides communication for the oil from the annular channel and thus the oil supply passage 4 to the reservoir 11.

The rod seat 35 has a central, downwardly extending stop 40. Surrounding the stop 40 is a disk shaped centrally domed spring 41. The spring 41 is convex and has a central aperture 42 so that it may seat about the stop 40 (Fig. 4). The periphery of the spring 41 is provided with several notches 43, permitting oil to ilow through the spring. The spring 41 is of a highly resilient spring steel and is so designed that its biasing force ex ceeds that of the plunger return spring 20 throughout the latter springs operating range. The shape and strength of the spring 41 must be such that it can separate the valve disk 28 from the stop 40 by about 0.004 of an inch. This is an arbitrary figure and considerable deviation from this figure is practical to meet the demands of particular cam designs.

While a domed spring is particularly suited to this particular operation, it will be recognized that other biasing means may be used. An example of a suitable substitute is a wave washer.

The entire internal structure of the tappet is prevented from disassembling from the tappet body by a snap ring 45 seated .in a suitable groove in the inner wall of the tappet body 2 adjacent its open end.

Modifications Fig. 5 illustrates a modification of this invention. The structure of this tappet is identical to that illustrated in Fig. l except for the structure of the relief valve and a slight modification of the rod seat. The tappet 1a has the same tappet body 2 and the external annular channel 5 and oil inlet port 39. The structure of the plunger 1t) and its related parts is also identical. However, a disk 50 having a central aperture 51 is substituted for the sealing ring. The circumferential edge of the disk is formed downwardly to provide an inclined sealing apron 52. The apron forms a tight seal against the walls of the tappet housing 2.

The downward sloping of the sealing apron S2 is such that when the pressure in the secondary pressure chamber 25 exceeds that of the oil on the other side of the sealing disk 50 the apron will be forced out into increasingly tighter sealing engagement with the interior walls of the tappet body. Thus, as the pressure differential increases, the seal effected by this apron increases correspondingly. The sealing disk 50 may be made from a relatively stiff sealing material such as a hard neoprene or it may be a metal stamping from a suitable material such as brass. Like the sealing ring, it is seated on the end of the plunger 10 and forms a seal with the valve seat 26.

The sealing disk 50 is backed and supported by a centrally apertured, cupshaped valve plate 53. The peripheral walls of the valve plate 53 project above its top inner surface, forming a circular pocket within which is seated the spring 54. The spring 54 is identical to the spring 41 in that it is convex and thus centrally domed. Like the spring 41, it has a plurality of peripheral notches 55 to permit the passage of oil through it. However, the spring 5'4 is not centrally apertured since the bottom of the rod seat 35a is smooth and has no stop. The spring 54 is of slightly lesser diameter than the inside diameter of the walls of the valve plate 53 so that it may be pressed and thus spread, permitting'the rod seat 35a to seat on the rim of the valve plate. The arch of the spring 54 is such that it is capable of separating the valve disk 53 and the rod seat 35a by about .004 of an inch. To prevent the seating of the valve seat on the rim of the valve plate from formingan oil seal, the lower edge of the rod seat is provided with one or more oil passages 56 (Figs. 5 and 7).

Fig. 6 illustrates a further modification of this invention. In this structure, the upper end of the plunger 10a is not of. reduced diameter to create a secondary pressure chamber. However, the end of the plunger is smoothly machined to provide a valve seat 26a for engaging the lower end of the valve ring 60. The valve ring 60 consists of a lower, annular collar portion 61 from the upper end of which projects a radially extending flange, the periphery thereof forming a sliding t with the interior surfaces of the tappet body 2. This forms a lower external chamber which constitutes the secondary pressure chamber 25a between the upper end of the plunger 10a and the under surface of the radially extending ange 62. Seated within the secondary pressure chamber is a suitable sealing member 63 such as an O-ring.

The peripheral portion of the ange 62 has an upstanding rim 64 for engaging the lower surface of the rod seat 35a. The upper surface of the radially extending flange 62 in cooperation with the rim 64 forms a pocket for seating the spring 54. The spring 54 is designed normally to separate the rod seat 35a from the upper surface of the valve ring 60 a distance approximately .004 of an inch. The rod seat 35a has no central stop and is equipped with an oil passage 55. The valve ring 60 is centrally apertured to provide free access to the oil reservoir 11.

Operation v l For the purposes of describing the operation of `this invention, it is assumed that the tappet is in the positionv illustrated in Fig. 1 with the cam 70 rotating in the direction indicated by the arrow. The'cam-70 isof conventional design and is typical of those used to open the valve of an explosion engine.

In the position illustrated in Fig. l, the tappet is motionless since it is still contacting that portion of the cam surface which is of constant radius. In this position, the forces within the tappet are in balance. Thel rod 37 is limited from further downward movement `by conventional structure not illustrated. The rod seat 35 and the relief valve plate 28 are separatedby the force of the relief valve spring 41 a short distance which in the normal valve trainwill not exceed approximately 0.004 of an inch.

In this position, the relief valve sealing ring-2,7 is seated firmly against the valve seat 26. Thus, a liquid tight seal is formed between the secondary pressure chamber 25 and the reservoir 11. This engagement is maintainedv by the upward biasing of the plunger return spring which returns the plunger upwardly until its movement is checked by the downward biasing of the relief valve spring 41. Since the relief valve spring 41 exerts a greater force than that of the plunger return spring 20,` the relief valve plate 28 will be spaced from the end of the stop 40.

The reservoir 11'is filled with oil under a positive pressure supplied through the oil passage 4 from any suitable source within the engine. The primary pressure chamber 13 is also lled with oil supplied from the reservoir through the disk valve 14. When the primary pressure chamber 13 is lled, the disk valve 14 automatically closes. The secondary pressure chamber is also filled with oil, thus establishing an equilibrium of forces throughout the interior of the tappet.

As the cam 70 initiates its opening movement of the valve by raising the tappet (Fig. 2), the first vfew thousandths of upward travel of the tappet will compress the relief valve spring 41 until the stop 40 on the bottom of the rod seat seats against the relief plate 28. This will be practically instantaneous since the oil trapped within the pressure chamber 13 is, for all practical purposes, incompressible and the force applied to the tappet body 2 by the cam 70 will be transmitted directly to the plunger 10. This will not result in hammering within the tappet since this adjustment is completed While the tappets movement is still very gradual.

After contact between the plate 28 and the stop 40 has been established, the rod 37 will be lifted against the downward bias of the engine valve spring (the latter not being illustrated since it is conventional in equipment of this type and forms no part of this invention).v Throughout the remainder of the rise and fall of the tappet as the crown 71 of the cam passes under it, all of the forces required to open the valve and control its closing movements will be transmitted through the plunger 10 to the relief valve sealing ring 27 at the valve seat 26. This assures the formation of a positive seal at this point, pery'body 2 continues to descend a few more thousandths of mitting no oil to escape from the secondary pressure chamber 25 to the reservoir 11 even though substantial pressures are built up. At the most, an insignificant quantity of oil will leak between the sealing ring 27 and the inner walls of the tappet body 2.

The forces involved in opening the valve and closing it against the valve spring as the cam passes through its actuating cycle will generate substantial pressures within the primary pressure chamber 13. These are immediately transmitted to the secondary pressure chamber 25 by leakage between the external surfaces of the plunger 10 and the internal walls of the tappet body 2. The clearances are sufficient that the forces in these two chambers will remain in substantial balance at all times.

During the last few thousandths of an inch of downward travel as the tappet comes to rest once more on the portion of constant radius of the cam 70, downward movement of the valve rod 37 is checked by a suitable stop, normally the seating of the valve, thus relieving the pressurev exerted upon the rod seat 35. As the tappet an inch, the high pressure existing in the secondary pressure -chamber 25 will overcome the force of the relief valve -spring 41, holding it in compressed position. This permits the sealing ring 27 to separate from the valve seat 26 at the end of the plunger 10. This condition occurring only momentarily, exists long enough to allow sutlicient oil to ow from the secondary pressure chamber 25 that the pressure within this chamber will be relieved to the Ypoint where the spring 41 may reassert itself and close the relief valve. This functions las a readjustment and equalizer of forces Within the tappet. Once again the forces acting throughout the tappet will be in balance. When a cold engine is rst started, the length of the valve train will be substantially shorter due to contraction than when the engine has been running for a period of time. The tappet on the rst one or two cycles will automatically adjust its length, if necessary, by drawing oil past the disk valve 14 into the pressure chamber 13 to expand its effective length suiciently to reect the contracted Condition of the valve train. However, during the initial period of engine operation, the valve train will rapidly warm up and las a result will expand. Thus, the tappet must subsequently progressively reduce its effective length to compensate for the expansion of the parts. This expansion occurs in small increments not exceeding 0.004 of an inch during each revolution of the cam 70 until the engine and the parts reach normal operating temperature. It is during this initial warm up period that it is necessary to discharge small quantities of the oil from the primary and secondary pressure chambers to effect reduction in the effective length of the tappet.

This invention automatically releases only that amount of oil from the pressure chamber necessary to re-establish the balance of forces within the tappet. Heretofore, no tappet has provided such an arrangement. The reduction in the effective length of the tappet has been controlled solely by close tolerance t between the plunger and the tappet body. In the ycase of .a rapid warm-up, this leakdown may not be enough to reduce the effective length of the tappet with corresponding rapidity, resulting in excessive forces being applied to the valve train. When the conventional tappet wears slightly, this leakdown may be too rapid, causing what is known as tappet noise when the valve is seated. It may also result in the tappets failure to fully open the valve. This causes power loss in the engine. Any microscopic foreign particles entering the conventional tappet may interfere with the proper functioning of the leakdown process and thus interfere with the tappets adjustment. y This invention eliminates all of these problems becaus a vlalve structure is employed to control the relief of pressure in the pressure chamber forming Aboth a positive seal during the actual operation of the tappet and a positive relief to `adjust forces at the end of each stroke.

Further, this invention effects the adjustment during the period of inactivity of the tappet not during the operating portion of the tappets cycle. This permits the adjustment to be made where it will not aifect the operation of the valve train` The closure of the gap normally maintained by the spring 41 between the relief valve plate 28 and the rod seat 35 occurs gnadually because it occurs at the very beginning of the change in radius of the cam where the rise of the tappet is gradual. Further, the short distance of travel required to close this gap is such that insuflicient speed will be built up between the two parts to produce any hammering. The spring 41 maintains fa resilient spacing between the effective length of the rod 37 and the remainder of the tappet, thus preventing any possibility of a binding iaction.

This is the rst tappet so constructed that the forces within the tappet always return to a pre-set balance of values during the inactive portion of the valve cycle. The structure of the tappet is such that this cannot be otherwise. Heretofore there was no assurance that the forces within the tappet would be re-established at a desired optimum at any point throughout the operating cycle of the valve train.

It will be understood that in order to open the relief valve it is necessary that the forces bearing against the` sealing ring 27 must exceed that of the spring 41 or the valve will not open.

The operation of the modified forms of this invention illustrated in Figs. and 6 is identical. In the case of the structure illustrated in Fig. 5, the lifting force to open the relief valve will be exerted against the apron 52 of the sealing member 50. In the case of the structure illustrated in Fig. 6, the lifting force is exerted against the scaling ring 63 to lift the valve ring 60.

This invention not only provides a hydraulic tappet of more positive and dependable operation, it provides a tappet which is considerably less costly to mantuacture. In the manufacture of conventional tappet structure, the plungers and bodies must be sorted in increments of 33 or 50 millionths of an inch and the matched pairs assembled. Practically any microscopic particle of dirt or metal caught between the plunger and the tappet body will cause the plunger to stick thus rendering the tappet ineffective. These problems are eliminated by this invention and a comparatively loose lit may be provided between the plunger andthe tappet body since this has nothing to do with controlling the leakdown of the tappet. This alone reduces manufacturing costs not only by eliminating the necessity for selective fit but also by eliminating the necessity for extremely precise mashining.

While there has been described a preferred embodiment of this invention and two modifications thereof, it will be understood that other modifications may be made. Such of these modiiications as incorporate the principles of this invention are to be considered as included in the hereinafter appended claims unless these claims by their language expressly state otherwise.

I claim:

l. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within said body and dividing the interior thereof into a pressure chamber and a reservoir; an element forming a seal between said pressure and reservoir chambers; a rod seat movably seated in said body between the open end thereof and said plunger; a compressible member bearing against said lrod seat and urging said element into seal forming position; said ele-ment being moved against saidv compressible member to breach said seal when said rod seat is spaced from said element and the force exerted by the uid in said pressure chamber against said element exceeds the force exerted by said compressible member against said element.

2. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within said body and dividing the interior thereof into a pressure chamber and 8 a reservoir; a valve seat at the end of said plunger remote from 'said pressure chamber; a valve element forming a seal with said valve seat between said pressure and reservoir chambers; a rod seat movably seated in said body between the open end thereof and said plunger; a compressible spring bearing against said rod seat and urging said valve element against sm'd valve seat; said valve element being moved against said spring to breach said seal with said valve seat when said rod seat is spaced from said valve element and the force exerted by the iiuid in said pressure chamber against said valve element exceeds the force exerted by said spring against said valve element.

3. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within said body and dividing the interior thereof into a primary pressure chamber and a reservoir; a secondary pressure chamber; said secondary pressure chamber communicating with said primary pressure chamber; an element forming a seal between said secondary pressure and reservoir chambers; said valve element forming one wall of said secondary pressure chamber; a rod seat movably seated in said body between the open end thereof and said plunger; a compressible spring bearing against said rod seat and urging said element into seal forming position; said element plate being moved against said spring to breach said seal when said rod seat is spaced from said element and the force exerted by the iiuid in said secondary pressure chamber against said element exceeds the force exerted by said spring against said element.

4. A hydraulic tappet as recited in claim 3 wherein said valve element has an annular sealing member and a rigid backing plate and said spring bears against said backing plate; stop means for limiting the closing movement between said rod seat and said backing plate before said spring is completely collapsed.

5. A hydraulic tappet as recited in claim 3 wherein said valve element is an annular collar; said collar having an inwardly opening step therein, intermediate its ends forming a recess for said spring; one end of said collar adapted to engage said rod seat; the depth of said recess being such that said rod seat and said one end of said collar engage before said spring is completely collapsed 6. A hydraulic tappet as recited in claim 3 wherein said valve element has an annular sealing member and a rigid backing plate and said spring bears against said backing plate; said backing plate being apertured to provide communication from said reservoir to the area of said body adjacent said rod seat; stop means for limiting the closing movement between said rod seat and said backing plate before said spring is completely collapsed.

7. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within said body and dividing the interior thereof into a pressure chamber and a reservoir; a rod seat movably seated in said body between the open end thereof and said plunger; a valve ring between said rod seat and said plunger; the one end of said valve ring adjacent said plunger being of reduced external diameter, the other end of said valve ring being of greater external diameter and slidably seating against the inner walls of said body; said one end of said valve ring and the inner walls of said body delining a secondary pressure chamber therebetween; a sealing ring seated in said secondary pressure chamber and adapted to prevent the escape of liquid therefrom; said one end of said valve ring being adapted to form a seal with the end of said plunger for isolating said secondary pressure chamber from said reservoir; a compressible spring bearing against said rod seat and urging said valve ring into seal forming position with said plunger; said valve ring being moved against said spring to breach said seal when said rod seat is spaced from said valve ring and the force exerted by the fluid in said secondary pressure chamber against said valve ring exceeds the force exerted by said springagainst said valve ring.

8. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within said body and dividing the interior thereof into a primary pressure chamber and a reservoir; a secondary pressure chamber; said secondary pressure chamber communicating with said primary pressure chamber; an element forming a seal between said secondary pressure and reservoir chambers; said element having a peripheral apron inclined radially outwardly and toward said plunger; said valve element and the apron portion thereof forming one wall of said secondary pressure chamber; a rod seat movably seated in said body between the open end thereof and said plunger; a compressible spring bearing against said rod seat and urging said element into seal forming position; said element being moved against said spring to breach said seal when said rod seat is spaced from said element and the force exerted by the Huid in said secondary pressure chamber against said element exceeds the force ex erted by said spring against said element.

9. A hydraulic tappet comprising: a hollow body open at one end; a plunger slidably seated within lsaid body and dividing the interior thereof into a primary pressure chamber and a reservoir; a secondary pressure chamber; said secondary pressure chamber communicating with said primary pressure chamber; an element forming a seal between said secondary pressure and reservoir chambers; said valve element forming one Wall of said secondary pressure chamber; a rod seat movably seated in said body between the open end thereof and said plunger; a central stop on said rod seat projecting toward said plunger; a backing plate for said valve element; a compressible spring bearing against said rod seat and urging said backing plate and said Valve element into seal forming position; said spring being centrally apertured and seated about said stop; said valve element and backing plate being moved against said spring to breach said seal when said stop is spaced from said backing plate and the force exerted by the fluid in said secondary pressure chamber against said valve element exceeds the force exerted by said spring against said valve element; said backing plate seating against said stop when said tappet is compressed.

10. In the method of adjusting the operative length of a hydraulic tappet containing a liquid, the steps which include: confining certain of the liquid in said tappet in a zone; simultaneously sealing said zone by pressure and compressing said tappet and transmitting the force of said compression through the liquid in said sealed zone; relieving the compression exerted on said tappet while retaining a substantial portion of the compressive pressure on said liquid; partially releasing the pressure sealing said zone to breach said seal and permitting some of said liquid to escape said zone; closing said seal when said seal closing and liquid pressures are in balance.

ll. A hydraulic tappet comprising: a hollow tappet body member closed at one end; a plunger member slidably disposed within said tappet body; said plunger forming a pressure chamber between the end thereof and the closed end of said tappet body member; said pressure chamber being inclusive of the annular space between said plunger and tappet body members; a rod seat member slidably disposed within said tappet body over said plunger member; said rod seat member closing said annular pressure chamber space; a reservoir chamber formed within said plunger and closed by said rod seat member; reservoir pressure responsive check valve means provided between said reservoir and pressure chambers near one end of said tappet body; and self closing check valve means provided between said chambers near the other end of said tappet body; said self closing check valve means being operative for the unidirectional control of the flow of hydraulic fluid from said pressure chamber to said reservoir in response to the unbalance of uid pressure conditions Within said tappet body during the operation thereof.

References Cited in the ile of this patent UNITED STATES PATENTS 2,468,332 Johnson Apr. 26, 1949 2,595,583 Johnson May 6, 1952 2,732,832 Engemann Jan. 3l, 1956 2,784,706 Humphreys Mar. 12, 1957 2,784,707 Skinner Mar. 12, 1957 

